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Topic: 7805 Voltage Regulator outputting no more than 3V (Read 550 times) previous topic - next topic

ccoris

Hey guys,

I'm a relative novice to circuitry, but I've been tinkering with some 7805 voltage regulators (specifically these: https://www.amazon.com/MCIGICM-voltage-regulator-Regulator-Positive/dp/B07BDFMQF6/ref=cm_cr_arp_d_product_top?ie=UTF8) for a simple circuitry project, and I realized that my regulator was seeming to cause some problems.  More specifically, it only outputs roughly 3V whether my input is a 12V source or a 9V battery, when obviously it should be outputting 5V.

I also tried testing it with no load attached (so maximum current shouldn't be an issue) and I'm still facing the same problem.  I'm using a 0.33 microfarad capacitor at the input and a 0.1 microfarad capacitor at the output, but it doesn't seem to change anything.

I've looked over the datasheet numerous times and can't identify what's wrong, and I've tested roughly half the pack of 15 regulators, and they all behave the exact same way.  It doesn't seem likely that all of them would be malfunctioning, but I don't know what I'm doing wrong.  I've used a multimeter to verify that both my power sources (12V and 9V) are accurate, so that doesn't seem like it's the problem either.

Any ideas?
Much appreciated.

jremington

#1
Aug 15, 2020, 04:23 am Last Edit: Aug 15, 2020, 04:27 am by jremington
What did you use for a load?

If you have wired it correctly, using the correct pinout (post a close up, focused photo of your setup), and measured the voltage with an accurate multimeter, then you may be the proud owner of counterfeit chips.

Counterfeits are quite common on Amazon, Alibaba, Banggood, etc. With Amazon, you should be able to return them.

ccoris

#2
Aug 15, 2020, 04:35 am Last Edit: Aug 15, 2020, 04:36 am by ccoris
I tried to clean things up and send as clear a photo as I could manage, but I guess it's possible that I got a bad package.  I've attached a photo.  The green wire is my output voltage, which is still measuring 3V with the red/black wires connected to a 9V battery.

jremington

#3
Aug 15, 2020, 05:10 am Last Edit: Aug 15, 2020, 05:13 am by jremington
I see no load resistor. Try adding one, 100 to 1K Ohms, from output to GND and measure the output voltage again. The regulator could be oscillating.

SteveMann

, then you may be the proud owner of counterfeit chips.
Or a mis-marked one.
Fritzing pictures are NOT schematics. I don't speak Fritzing.

Please do not ask for help by PM. I will not respond. If you need help, post a question on the appropriate forum.

Click on Add Karma if I helped you.

ccoris

I see no load resistor. Try adding one, 100 to 1K Ohms, from output to GND and measure the output voltage again. The regulator could be oscillating.
It seems that it's outputting a consistent 3V even with a load resistor (I tried several up to 1k ohms).  Maybe I did get a bad batch of regulators.

TomGeorge

Hi,
Have you measured your 9V when it is connected to the regulator?
Make C1 in your diagram 10uF.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

AJLElectronics

Make C1 in your diagram 10uF.


Why? That is likely to provoke it into hooting. A 10uF at the power source maybe, but the .33 and .1 at the pins are specified to stop the regulator taking off.

It looks like the regulators are either defective or are 3.3V.  Price on these regulators varies wildly, from a few pennies to a few pounds per unit. I am sure that there is a good reason for that!

nzl123

#8
Aug 15, 2020, 12:04 pm Last Edit: Aug 15, 2020, 12:10 pm by nzl123
Try to replace battery in the multimeter. Or better try measurements with another multimeter. Maybe this one is somehow defective when measuring lower range voltage. I have never experience any of 7805 are fake no matter on sellers price, anyway these regulators are dirty cheap.

Do you have any older 7805, 78L05 or even board with? Can you test it with the same multimeter? Indeed, otherwise you may got a stock of fake ICs.

jremington

Quote
a consistent 3V even with a load resistor
Return them, with a complaint to Amazon.

ccoris

Try to replace battery in the multimeter. Or better try measurements with another multimeter. Maybe this one is somehow defective when measuring lower range voltage. I have never experience any of 7805 are fake no matter on sellers price, anyway these regulators are dirty cheap.

Do you have any older 7805, 78L05 or even board with? Can you test it with the same multimeter? Indeed, otherwise you may got a stock of fake ICs.
I know it's not a multimeter issue because I've verified the measurement, and the voltage it's outputting was causing problems in the circuit I was working on (where I had components that required 5V).  I think the next step is to try to return these and buy from another seller.

hammy

1.Check you've wired the pins up correctly
2.add some form of load resistor as mentioned -1k or some such
3. Check the input voltage as well as the output - the 9v battery may not be giving 9v when in circuit .
4. Check the chip numbers are correct ( google them )
5 . Maybe you have 3v regulators as someone suggested

MarkT

Don't buy chips/components from eBay or Amazon, unless you know the vendor.
So many are fake/pulls/inferior substitutes these days.

Proper electronics suppliers are the place to go, the big ones or the hobby specialists, they
have a reputation to maintain and are _very_ aware of the issue.  Amazon and eBay don't
have the means to deal with this it seems, you may be able to get a refund through them though.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

TomGeorge

#13
Aug 16, 2020, 03:44 am Last Edit: Aug 16, 2020, 03:46 am by TomGeorge
Hi,
Read the first question in post #6 please.

What sort of capacitors were you using?
They look like Tantalum, if so have you got them connected the right way around?

Thanks.. Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

runaway_pancake

"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

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